1. Field of the Invention
The present invention relates to an image processing method which offers excellent image erasability by being capable of expanding image recording and image erasing areas, ensuring sufficient image-erasing time and complete image erasing, and to an image processing apparatus using the image processing method.
2. Description of the Related Art
A non-contacting laser based method is proposed as a method of creation or deletion of an image on or from a thermoreversible recording medium (hereinafter referred to as “reversible thermal sensitive medium,” “recording medium,” or “medium” in some cases) whose surface has irregularities and as a method of creation or deletion of an image on such a medium at a distance (see Japanese Patent Application Laid-Open (JP-A) No. 2000-136022). This method adopts non-contacting recording on shipping containers used for distribution of goods, wherein the containers are formed of a thermoreversible recording medium, a laser is used for recording (writing) of image, and hot blast, heated water, infrared heaters, or the like are used to erase the image.
There are various proposed methods that involve laser irradiation for recording/erasing of image on/from such thermoreversible recording media (see for instance JP-A No. 07-186555 (Japanese Patent (JP-B) No. 3350836), JP-A No. 07-186445 (JP-B No. 3446316), JP-A No. 2002-347272, and JP-A No. 2004-195751).
The technique disclosed in JP-A No. 07-186555 (JP-B No. 3350836) is an improved method for image formation and erasing that involves formation or erasing of image on or from a thermoreversible recording medium by utilizing heat generated by irradiation of a photothermal conversion sheet placed on the medium with a laser beam. The Specification of the Patent Literature discloses that formation and erasing of image is possible by controlling the condition for laser beam irradiation. More specifically, it is stated that it is possible to control a heating temperature to a first specified temperature and a second specified temperature for the thermoreversible recording medium by controlling at least one of light irradiation time, light intensity, degree of focusing and light intensity distribution, and that it is possible to form or erase an image or partially entirely by changing the cooling rate after heating.
JP-A No. 07-186445 (JP-B No. 3446316) discloses a method that uses two laser beams: one as an oval or oblong laser spot for image erasing, and one as a circular laser spot for image formation, a method for recording using a composite beam of two lasers, and a method for recording using a composite beam of two transformed lasers. Two laser-recording can realize high-density image formation compared to one laser-recording.
The technique disclosed in JP-A No. 2002-347272 is directed to utilize during image recording or erasing both sides of a mirror to change the shape of the focused laser beam spot according to the differences in optical paths and/or mirror shape, whereby it is possible to change the size of a beam spot or to make the beam out of focus with a simple optical system.
Furthermore, JP-A No. 2004-195751 discloses that almost all the ghost images remained after image erasing can be removed by setting the laser absorbance of a label-shaped reversible thermosensitive recording medium to 50% or more, irradiation energy during printing to 5.0 mJ/mm2 to 15.0 mJ/mm2, a product of laser absorbance and irradiation energy for print to 3.0 mJ/mm2 to 14.0 mJ/mm2 and a product of laser absorbance upon erasing and irradiation energy for print to 1.1 folds to 3.0 folds.
In addition, a method of erasing of an image using a laser beam is proposed (see JP-A No. 2003-246144), wherein recording of a clear-contrast image of high durability is said be realized on reversible thermosensitive recording media by erasing previous one at levels (laser beam energy, laser irradiation time, scanning speed and pulse width) that are 25% to 65% of those for laser recording.
Laser printing and laser erasing can be performed by the methods described above. However, in cases where an image is printed on or erased from a thermoreversible recording medium extensively and where a thermoreversible recording medium is attached to a delivery container used for distribution lines for non-contact recording thereon, it results in failure to achieve complete image recording, in particular image erasing, due to energy shortage in the laser beam, depending on the distance between the medium and the laser source-equipped image recording apparatus and/or on the passing speed of the medium on the line.
There are proposed methods for solving the foregoing problems that involve use of an apparatus capable of focus control, wherein the laser beam energy level is independent of the distance between the thermoreversible recording medium and the laser source-equipped image recording apparatus. For example, Japanese Utility Model Application Laid-Open (JP-U) No. 56-27936 and Japanese Patent Application Laid-Open (JP-A) No. 58-83812 (Japanese Patent Application Publication (JP-B) No. 03-81133) disclose focus controlling by deforming a mirror. With this method the foregoing problems can be solved.
The methods described above, however, has a problem of requiring a special device for mirror deformation and thus cannot be applied to general laser devices.